This invention relates to an image reading apparatus and method suitable for use with facsimilies, copiers, image scanners or the like.
Pseudo halftone methods have been employed to reproduce halftone gradations by changing the density of black or white pixels (picture elements). A typical pseudo halftone method is suggested by T. H. Morrin in his paper entitled "A Black-White Representation of a Gray-Scale Picture" published Feb., 1974, in IEEE TRANSACTIONS ON COMPUTER, C-23 at pp. 184-186. Another pseudo halftone method is suggested by B. E. Bayer in his paper entitled "An Optimum Method for Two-Level Rendition of Continuous-Tone Pictures" published in 1973, in ICC CONF RECOND at pp. 2611-2615. These pseudo halftone methods, which convert a read image into a display signal using one-bit to represent each pixel, permit the use of a simple signal processing technique and their applications to printers, facsimilies or the like displaying white/black images. Although such conventional pseudo halftone methods have a capacity for good tone reproduction characteristics, they exhibit poor resolution in some cases, particularly in line-copy reproduction, as described later in greater detail.